180 



ANATOMY OF THE HEAD. 



prominence and beauty to the orb ; while the orbits them- 

 selves are lined by a periosteum furnished by the dura 

 mater. 



FIG 19. 



DIAGRAM OF THE EYE. 



9, The retina. 

 a, The tunica vorticosa. 

 h, The secreting membrane of the cho- 

 roid. 

 c, The pigmentum nigrum. 

 e, The tunica Jacobi. 

 /, The expansion of the optic nerve. 

 g. The arterial tunic of the retina. 



The black spots upon either side of the 



pupil, at the corpora nigra. 

 The thin lines denote the course of a 



ray of light. 

 The large lighter space is the tapidum 

 lucidum. 



0, The optic nerve. 

 /, The ophthalmic artery. 



1, The aqueous humour. 



2, The crystalline humour and lens. 



3, The vitreous humour. 



4, The hyaloid membrane, which secretes 



the vitreous humour. 



5, The capsule of the lens, kept in its situa- 



tion by the hyaloid and aqueous 

 membranes. 



6, The aqueous membrane, which secretes 



the aqueous humour behind the 

 cornea. 



7, The sclerotic coat. 



8, The choroid coat. 



The humour of the eye, upon which the round shape 

 of the globe mainly depends, are three in number ; the 

 aqueous, which is most forwardly situated (Fig 19 . 1). 

 The crystalline, which occupies the middle place {Fig 19 . 

 2) ; and the vitreous, holds the most backward or deep- 

 seated position {Fig 19.3). Of the three, the vitreous 

 is by very far the largest. The aqueous is the next in 

 amount, though able to bear no comparison with the 

 vitreous ; and the crystalline is the least in quantity. In 

 density, the crystalline is by very far the most dense. The 

 aqueous and vitreous being equal in this respect, and in 

 the physical qualities resembling the clearest water. But 

 why then is one called the vitreous ? Because some of the 



